The present invention relates to position and orientation determination using stationary fan beam sources and rotating mirrors to sweep fan beams. The present invention has applications in diverse areas such as medicine, aerospace, and virtual reality. Additionally, the present invention may be employed for position and orientation monitoring of surgical instruments, for cockpit-based helmet mounted siting mechanisms, and for augmented reality computer-aided design.
It is generally known in the prior art to provide a system in which position and orientation measurements are carried out using multiple scanning beams in a reference frame and multiple detectors mounted on a movable object. An example of such a system is disclosed in U.S. Pat. No. 5,767,960 to Orman. Such systems measure beam times of arrival and compute the positions of the various detectors using a technique known as triangulation.
In the prior art, systems have employed the use of three scanning fan-shaped beams, each of which originates from a separate scanning mirror station which deflects the fan beams across a measurement space. The cost and complexity of multiple scanning units makes these approaches commercially impractical. Applicant is aware of the following U.S. Patents:
U.S. Pat. No. 5,100,229 to Dornbusch
U.S. Pat. No. 5,128,794 to Mocker
U.S. Pat. No. 5,187,540 to Morrison
U.S. Pat. No. 5,268,734 to Parker
U.S. Pat. No. 5,767,960 to Orman.
Parker and Dornbusch use three scanner mirrors and laser sources to measure angles of inclination from three source points. Orman measures position of a detector using three fan beams rotating about one axis but Orman requires an awkward arrangement of optical fan beam sources with the sources rotating about a common axis.
The present invention differs from the teachings of the prior art listed above in that, in the present invention, the fan beam sources are stationary and are directed toward one or more rotating mirrors with the fan beams reflected from the mirrors moving through a measuring space in a controlled predictable manner.
The present invention relates to position and orientation determination using moving means comprising stationary fan beam sources and rotating mirrors to sweep fan beams. The present invention includes the following interrelated objects, aspects and features:
(1) In a first embodiment, motor means comprises a single motor having drive shaft means comprising an elongated drive shaft. In one aspect, the drive shaft has preferably mounted thereon reflector means comprising two mirrors, the reflective faces of which lie in common planes. If desired, the reflector means can comprise a single elongated mirror. In any event, the reflective surfaces thereof should be in a common plane.
(2) In the preferred embodiment of the present invention, each reflective face of each mirror is generally rectangular and the reflective faces or facets face in diametrically opposite directions spaced 180xc2x0 apart. If desired, the shaft may be provided with a single elongated mirror having one or more faces or some amount of mirrors greater than two mirrors. If desired, four reflective faces spaced 90xc2x0 apart may be employed.
(3) Fan beams are generated in the first embodiment through the use of stationary laser beam sources which are aimed at each mirror. As the mirrors rotate, each stationary source is reflected off a particular mirror and into a measuring space in a predictable pattern of movement.
(4) The control means incorporated in the first embodiment of the present invention is provided with knowledge as to the rotative position of the mirrors at any given time.
(5) Sensor means comprising a sensor is attached to the object to be measured, which sensor is able to detect the time of arrival of impinging scanning beams. At least one of the fan-shaped beams is skewed with respect to other beams, and at least two of the fan-shaped beams have origins sufficiently separated to allow accurate triangulation of the position of the sensor over various regions of the measuring space. In this way, accurate measurement of position and orientation may be carried out.
(6) Computing means determine reflected fan beam planes from knowledge of incident fan beam planes and mirror positions corresponding to detector times of arrival. As is familiar to those skilled in the art, the reflected beam angle with respect to the mirror normal is equal to the incident beam angle. Detector position is computed as the intersection of three beam planes, as is a well known procedure to those skilled in the art. The positions of three detectors are used to define a plane, from which the sensor orientation is determined, also a familiar procedure to those skilled in the art. In this way, the sensor position and orientation (6DOF) is determined.
(7) In a second embodiment of the present invention, motor means comprises separate drive motors, each of which carries reflector means comprising a mirror with the drive shafts of the motors preferably being parallel to one another and with the reflective surfaces of the mirrors lying in either common planes or parallel planes. In this regard, at two positions of the respective drive shafts of the motors, reflective surfaces of the mirrors lie in common planes. As the mirrors rotate from those positions, at other orientations thereof, the mirrors lie in parallel planes.
(8) In the same way as is the case in the first embodiment, fan-shaped beams are generated through stationary sources of laser beams that are directed at the reflective surfaces of the mirrors and thence reflect into the measuring space. Each mirror may consist of a single reflective surface or a plurality of reflective surfaces such as two opposed surfaces or four surfaces where each reflective surface is related to adjacent reflective surfaces by a right angle.
(9) In the control means of the present invention electrical circuitry is incorporated in the second embodiment and provided with knowledge of the rotative position of each shaft and reflective surface and the sensor detects times of arrival of the various fan-shaped beams. With the shafts of the two motors spaced sufficiently apart and with at least two of the fan-shaped beams skewed with respect to one another, the control means is programmed so that triangulation may be carried out to determine the position and orientation of an object within the measuring space.
(10) Computing means determine reflected fan beam planes from knowledge of incident fan beam planes and mirror positions corresponding to detector times of arrival. As is familiar to those skilled in the art, the reflected beam angle with respect to the mirror normal is equal to the incident beam angle. Detector position is computed as the intersection of three beam planes, as is a well known procedure to those skilled in the art. The positions of three detectors are used to define a plane, from which the sensor orientation is determined, also a familiar procedure to those skilled in the art. In this way, the sensor position and orientation (6DOF) is determined.
As such, it is a first object of the present invention to provide position and orientation determination using stationary fan beam sources and rotating mirrors to sweep fan beams.
It is a further object of the present invention to provide such a system wherein, in a first embodiment thereof, mirrors are rotatably mounted on a common shaft rotated by a single motor.
It is a still further object of the present invention to provide such a system in a second embodiment thereof in which a plurality of motors are provided with their shafts parallel to one another and with each shaft rotating a mirror having one or more reflective surfaces.
It is a still further object of the present invention to provide such a system wherein, in each embodiment thereof, the angular position of the motor shaft or shafts is/are known.
It is a still further object of the present invention to provide such a system wherein knowledge of rotative shaft position and times of arrival of fan-shaped beams at an object are used to measure position and orientation of the object in a measuring space or work area.
These and other objects, aspects and features of the present invention will be better understood from the following detailed description of the preferred embodiments when read in conjunction with the appended drawing figures.